Membranes polymeric synthetic

Kestig RE. Phase-Inversion Membranes in Synthetic Polymeric Membranes A Structural Perspective. New York John Wiley Sons, 1985, pp. 237-286. 

In a study of the interaction of three different membranes, two synthetic polymers and cellulose, and solutions containing diflferent concentrations of dextrose, was evaluated the relative reduction of water flow, given in percentage, the difference between the flow before and after solute adsorption divided by flow prior to adsorption. In SG-PES and PES-GR polymeric membranes, water flux declined of about 4%-12% and 11%-15% respectively, while for the cellulose membrane was not observed a significant reduction in the flow, indicating a significant adsorption of dextrose on the surface of membranes made of synthetic polymers (more hydrophobic). The significant difference in the rednction of the flow in the membranes of synthetic polymers is dne to differences in the characteristics of the membrane surface [12]. 

This book is devoted to synthetic, or artificial, membranes. In particular, our focus will be on polymeric synthetic membranes, since most industrial membranes belong to this category. Before entering the main subject of this book, i.e., atomic force... 

In the search for PEMs with lower alcohol permeability than Nafion and other perfuorinated membranes, without degradation of the proton conductivity, a number of new polymeric membranes were synthetized and characterized, such as sulfonated polyimides, poly(arylene ether)s, polysulfones, poly(vinyl alcohol), polystyrenes, and acid-doped polybenzimidazoles. A comprehensive discussion of the properties of these alternative membranes is given in Chap. 6, along with those of Nafion and Nafion composites. 

To overcome the problems of cellulose acetate membranes, many synthetic polymeric materials for reverse osmosis were proposed, but except for one material, none of them proved successful. The only one material, which could remain on the market, was the linear aromatic polyamide with pendant sulfonic acid groups, as shown in Figure 1.2. This material was proposed by DuPont, which fabricated very fine hollow fiber membranes the modules of this membrane were designated B-9 and B-10. They have a high rejection performance, which can be used for single-stage seawater desalination. They were widely used for mainly seawater or brackish water desalination and recovery of valuable materials such as electric deposition paints, until DuPont withdrew them from the market in 2001. 

More recendy, two different types of nonglass pH electrodes have been described which have shown excellent pH-response behavior. In the neutral-carrier, ion-selective electrode type of potentiometric sensor, synthetic organic ionophores, selective for hydrogen ions, are immobilized in polymeric membranes (see Membrane technology) (9). These membranes are then used in more-or-less classical glass pH electrode configurations. 

R. E. Kestiug, Synthetic Polymeric Membranes, 2nd ed., John Wiley Sons, Inc., New York, 1985. 

Polymeric Ma.teria.Is, The single-ply membranes are made from a wide variety of polymers. The following is a brief description of those polymers and their characteristics. There are three thermosetting-type elastomeric membranes as of this writing (1996) neoprene, CSPE, and EPDM. Neoprene is stiU used where oil resistance is needed. Eor instance. Hydrotech uses neoprene flashings, the base of which is hot-set in mbberized asphalt (see ElASTOL RS, SYNTHETIC-POLYCm.OROPRENE). 

S. Hwang and K. Kammermeyer, Membranes in Separations,]ohn Wdey Sons, Inc., New York, 1975 good study of membrane transport phenomenon. R. E. Kesting, Synthetic Polymeric Membranes, McGraw-HiU, New York, 1971 good bibhographies. 

Membranes used for the pressure driven separation processes, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO), as well as those used for dialysis, are most commonly made of polymeric materials. Initially most such membranes were cellulosic in nature. These ate now being replaced by polyamide, polysulphone, polycarbonate and several other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation.11 This process has four main steps ... 

Polymeric vesicles could be of better use for such an antitumor therapy on a cellular level, since they have at least one of the properties required, namely an extraordinary membrane stability. For a successful application, however, the simple systems prepared so far must be varied to a great extent, because the stability of a model cell membrane is not the only condition to be fulfilled. Besides stability and possibilities for cell recognition as discussed above the presence of cell membrane destructing substances such as lysophospholipids is necessary. These could e.g. be incorporated into the membrane of stabilized liposomes without destruction of the polymeric vesicles. There have already been reports about thekilling of tumor cells by synthetic alkyl lysophospholipids (72). 

Figure 15. Schematic of the build up of stable cell models via partial polymerization of the membrane. Key

One of the extensively used synthetic polymers used as a support for immobilization of biocatalysts is polyacrylamide (PAAm) [287,288], The major advantage is that it can be polymerized either chemically or by using radiation. Advantages of y-ray polymerization against chemical polymerization is that the polymerization can be carried out even under frozen conditions thus allowing the matrix to be molded to any form such as beads or membranes [289-291], However one of the major drawbacks of this polymer especially in a membranous form is its brittleness. 

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